Characterization of circulating CD4+ CD8+ lymphocytes in healthy individuals prompted by identification of a blood donor with a markedly elevated level of CD4+ CD8+ lymphocytes.

During flow cytometric analysis of lymphocytes from healthy donors, we identified a donor (donor A) with 22% CD4+ CD8+ cells (versus values of < 4% for 65 other controls). To determine if CD4+ CD8+ cells from donor A and other controls were similar, we first defined the phenotypic profile of control CD4+ CD8+ cells. Enriched CD4+ CD8+ cell populations for 10 controls were prepared by a two-step positive selection scheme with anti-CD4-coated magnetic beads and anti-CD8-coated culture flasks; the selected population averaged 69% CD4+ CD8+ cells and 31% CD4+ CD8- cells. For all 10 controls, two subsets of CD4+ CD8+ cells, CD4dim CD8bright and CD4bright CD8dim, were observed. Phenotypic profiles of these two CD4+ CD8+ subsets were defined by pairing anti-CD8 with other monoclonal antibodies, and the profiles were compared with each other and with those of CD4+ CD8-, CD4- CD8bright, and CD4- CD8dim cells. CD8bright and CD4bright CD8dim cells differed in their proportions of CD62-L+ cells and in their levels of CD11a and CD2 expression. Both CD4+ CD8+ subsets resembled CD4+ CD8- cells in CD45RA, CD45RO, and CD25 expression; the comparable CD- CD8+ cells in CD62-L expression; and CD4- CD8bright cells in CD11b, CD11b, CD16/56, and CD28 expression. CD38 expression in both CD4+ CD8+ subsets was decreased compared with those of other cell subsets. Whereas control CD4+ CD8+ cells averaged 33% CD4dim CD8bright, CD4+ CD8+ cells from donor A were > 90% CD4dim CD8bright. Donor A CD4dim CD8bright cells exhibited proportional decreases in CD25 and CD62-L expression and increases in CD11b and CD54 expression compared with those of control CD4dim CD8bright cells.(ABSTRACT TRUNCATED AT 250 WORDS)